Madeline Wimmer- UMN Fruit Production Extension Educator
- Apples
- Growth stage update: pink- bloom.
- Considerations for fruit thinning during bloom
- Grapes
- Growth stage update:
- Early-season shoot thinning.
- Raspberries
- Raspberry cane diseases
- Honeyberries
- Growth stage update: bloom, and pollination compatibility
Apples
Images: (Left) Pink is the growth stage that occurs right before bloom, in apples. Here shows an apple bud in late-pink. (Right) Apples begin to bloom with one main flower, known as the king flower, emerging into full bloom before other blossoms. Photos taken at ApplesRus Orchard in Olmsted County (Zone 5a, 05/05/25).
Growth stage update: Pink - King bloom.
Pink! Is the apple landmark growth stage following tight cluster. This is the phase where the apple floral buds are continuing to develop, while surrounding leaves grow larger in size. Pink is the sign that bloom is just around the corner, which indicates the need to start thinking about pollination and hive management for orchards who supplement pollination with honey bees. This is also a good time to have a plan ready to go for chemical thinning programs, which can happen during or after bloom.Many varieties in SE Minnesota orchards are somewhere between pink and the starting phase of bloom where king blossoms flower before other floral buds unfold. Because it's the first blossom to unfold, it is also the first blossom to finish pollination and usually produces the largest fruit.
Considerations for fruit thinning during bloom
Bloom thinning is a method of reducing apple crop load during flowering, using specific thinning products that disrupt pollination in flowers that are not needed for this year’s crop. If the idea of bloom thinning is new to you as a grower, don't worry, as it's more commonly practiced in Minnesota to thin fruit after petal fall.
However, bloom thinning can be helpful for varieties like Honeycrisp that are prone to biennial bearing, and some products that thin during bloom are allowable under USDA Organic regulations (e.g., lime sulfur, ATS), which can be an advantage for organic fruit growers.
This week we’ve included an additional article in our newsletter on bloom thinning and how to use a pollen tube growth model:
Article: Bloom thinning apples: How the pollen tube growth model works.
Pest highlight: Codling moth (common pest)
A number of different lepidopteran pests (these are insects that become moths) are pests of apples, like red and oblique banded leaf rollers, oriental fruit moth, and codling moth. Of these, codling moth is a major pest of apples in the Upper Midwest. Codling moths overwinter as full-grown, protected larvae, and the adults tend to mate in the spring around bloom time, after which point the female adults will lay eggs near apple fruitlets. When those eggs hatch, the codling moth larva emerges and enters a nearby apple where it continues to grow and develop. Classic signs of codling moth infestation include an exit hole (sometimes close to the calyx), which is often referred to as a “sting,” when small, and can show frass on the outside as further evidence.
Trapping is used as a means to monitor the arrival of codling moth adults. The most effective traps are delta traps or wing traps with codling moth pheromone. These traps can be set out at eye-level around bloom time, and checked once every three days. Codling moth adults can be distinguished from other moths by a dark copper-brown band located at their wing tips. When 2-5 moths are caught per trap for at least two trap checks in a row, this marks the biofix date when degree days accumulations are counted. Around 200-250 degree days after the biofix date is when peak egg hatch occurs and management is recommended to begin.
Growers should keep in mind that codling moths typically have a second generation that begins in July in Minnesota, which should be considered when planning management this year. Depending on the weather during a given year, a third generation may also develop, although this is less common, especially in northern regions.
Management:
Non-chemical management for codling moths includes mating disruption, which is done during the first adult flight around bloom. Support for codling moth mating disruption can be found on page 25 of the Midwest Fruit Pest Management Guide, where information about different dispersal methods is available. Note that mating disruption is usually most effective for orchards that are 5+ acres in size.
Additional practices include removing fall fruits from the orchard throughout the growing season, and encouraging parasitoid populations through careful insecticide selection and avoiding broad-spectrum insecticides. Granulosis virus is another management option allowable under USDA Organic guidelines, along with oil applications to target codling moth eggs (i.e., ovicide).
Conventional chemical management options can be found in the Midwest Fruit Pest Management Guide, starting on page 34.
Images: (Left) Wooly bud without any leaf tips/green visible, (middle) further developed woody bud with green showing, and (right) buds forming beneath a removed spur that can be saved for future year spur replacement.
Images: Honeyberry flowers are tubular with the ovaries positioned below the flower, a feature known inferior ovaries. Honeyberry flowers benefit from cross pollination and are also known for their hardiness. Photos taken at Firefly Berries in Olmsted County, MN (Zone 5a).
Honeyberries, also known as haskap, are considered an emerging crop in the Upper Midwest. Most of the research and varietal development has been done at the University of Saskatchewan, which offers a rich library of honeyberry production resources. Honeyberry plants are unique as they can tolerate extreme winter temperatures and are one of a few crops that can thrive in regions as cold as USDA hardiness zone 2. They are related to other plants in the honeysuckle (Lonicera) genus, and do not indicate invasiveness like some other honeysuckle species.
The above chart is courtesy of Gary Wyatt, UMN Extension Educator.
Trapping is used as a means to monitor the arrival of codling moth adults. The most effective traps are delta traps or wing traps with codling moth pheromone. These traps can be set out at eye-level around bloom time, and checked once every three days. Codling moth adults can be distinguished from other moths by a dark copper-brown band located at their wing tips. When 2-5 moths are caught per trap for at least two trap checks in a row, this marks the biofix date when degree days accumulations are counted. Around 200-250 degree days after the biofix date is when peak egg hatch occurs and management is recommended to begin.
Growers should keep in mind that codling moths typically have a second generation that begins in July in Minnesota, which should be considered when planning management this year. Depending on the weather during a given year, a third generation may also develop, although this is less common, especially in northern regions.
Management:
Non-chemical management for codling moths includes mating disruption, which is done during the first adult flight around bloom. Support for codling moth mating disruption can be found on page 25 of the Midwest Fruit Pest Management Guide, where information about different dispersal methods is available. Note that mating disruption is usually most effective for orchards that are 5+ acres in size.
Additional practices include removing fall fruits from the orchard throughout the growing season, and encouraging parasitoid populations through careful insecticide selection and avoiding broad-spectrum insecticides. Granulosis virus is another management option allowable under USDA Organic guidelines, along with oil applications to target codling moth eggs (i.e., ovicide).
Conventional chemical management options can be found in the Midwest Fruit Pest Management Guide, starting on page 34.
Grapes
Growth stage update: Wooly bud with and without green showing
Images: (Left) Wooly bud without any leaf tips/green visible, (middle) further developed woody bud with green showing, and (right) buds forming beneath a removed spur that can be saved for future year spur replacement.
When tracking grapevine growth stages, the Fruit Update series follows the modified E-L system.
Similar to other fruit crops, cold hardy grape varieties show variation in bud development. This week, many grape varieties have developing buds with those further along reaching the wooly bud either without, or with some green showing beneath the fibers, indicating the bud is closer to bud break and shoot emergence.
The following vineyard tasks can be done at this time:
Image: Two photos of a raspberry canes that had been infected the previous growing season with a raspberry cane disease.
The frequent wet periods that occurred at the beginning of the 2024 growing season created a good environment for fungal pathogens to cause infections on fruit crops. This past week, I’ve been monitoring lateral shoot development for a stand of summer-bearing (i.e., floricane producing) raspberries that had a cane infection on the developing primocanes in 2024. The current infection symptoms include visual discoloration from lesions, along with cracking bark.
Cane blight (pathogen: Leptosphaeria coniothyrium), spur blight (pathogen: Didymella applanata), and anthracnose (pathogen: Esinoe venata) are all examples of raspberry cane diseases with distinct infection symptoms from shoot dieback, to lesions on canes and leaves, and cracking on canes.
Managing diseased canes will depend on which disease they have and how extensive the infections are. If it’s possible to remove and destroy infected canes, this will help reduce the inoculum of overwintering pathogens that are present. Prune healthy production regions before moving to infected areas, and avoid pruning and topping canes during wet weather. Information about chemical management options can be found in the Midwest Fruit Pest Management Guide starting on page 208.
Resources:
The following vineyard tasks can be done at this time:
- Clean up any remaining canes and mummified clusters left over from winter pruning and the previous growing season.
- Take time to check wires and tighten loose wires as needed.
- Continue to check any bands or ag-ties while out in the vineyard that may need adjusting. Continue to scout for grape flea beetles, especially near wooded edges.
- Have a plan ready to go for early-season disease management.
- Schedule time on your calendar to make a pass through the vineyard when shoots are around 4-6 inches tall, and thin shoots to 6-8 shoots per linear foot, depending on your vineyard needs, after shoot emergence has occurred. Check back next week for more best practices related to shoot thinning.
- To learn more about grape flea beetles, check out this recent Fruit Update article.
- For more information on early-season vineyard diseases, refer to the grape section in our previous Fruit Update article.
Raspberries
Raspberry cane diseases
Image: Two photos of a raspberry canes that had been infected the previous growing season with a raspberry cane disease.
The frequent wet periods that occurred at the beginning of the 2024 growing season created a good environment for fungal pathogens to cause infections on fruit crops. This past week, I’ve been monitoring lateral shoot development for a stand of summer-bearing (i.e., floricane producing) raspberries that had a cane infection on the developing primocanes in 2024. The current infection symptoms include visual discoloration from lesions, along with cracking bark.
Cane blight (pathogen: Leptosphaeria coniothyrium), spur blight (pathogen: Didymella applanata), and anthracnose (pathogen: Esinoe venata) are all examples of raspberry cane diseases with distinct infection symptoms from shoot dieback, to lesions on canes and leaves, and cracking on canes.
Managing diseased canes will depend on which disease they have and how extensive the infections are. If it’s possible to remove and destroy infected canes, this will help reduce the inoculum of overwintering pathogens that are present. Prune healthy production regions before moving to infected areas, and avoid pruning and topping canes during wet weather. Information about chemical management options can be found in the Midwest Fruit Pest Management Guide starting on page 208.
Resources:
- For more information, see our UMN web page, “Raspberry cane diseases.”
- Information about our UMN Plant Disease Clinic can be found here.
Honeyberries
Growth stage update: Bloom, and pollination compatibility
Images: Honeyberry flowers are tubular with the ovaries positioned below the flower, a feature known inferior ovaries. Honeyberry flowers benefit from cross pollination and are also known for their hardiness. Photos taken at Firefly Berries in Olmsted County, MN (Zone 5a).
Honeyberries, also known as haskap, are considered an emerging crop in the Upper Midwest. Most of the research and varietal development has been done at the University of Saskatchewan, which offers a rich library of honeyberry production resources. Honeyberry plants are unique as they can tolerate extreme winter temperatures and are one of a few crops that can thrive in regions as cold as USDA hardiness zone 2. They are related to other plants in the honeysuckle (Lonicera) genus, and do not indicate invasiveness like some other honeysuckle species.
Table 1. Honeyberry pollination compatibility chart based on bloom windows, where the row and column labels represent common honeyberry varieties, and where they meet indicates whether or not there is overlap during bloom.
The above chart is courtesy of Gary Wyatt, UMN Extension Educator.
This week in SE Minnesota some varieties of honeyberries are in bloom. Knowing a honeyberry variety’s bloom window is helpful when determining which varieties are compatible for cross pollination. If there is no overlap in bloom times, pollination generally decreases as both variety's flowers need to have viable pollen, accessible to pollinators, and fully developed and exposed female flower parts to receive the pollen. For those who are looking planning to plant a new honeyberry stand considering varietal selection and layout during planting can be beneficial.
Resources:
Haskap compatibility, flowering, and ripening charts for U of SK Varieties (University of Saskatchewan)
Thank you to our farm and ag professional partners for contributions to the UMN Fruit Update series. Non-credited photos in this article were either taken by Madeline Wimmer or within the UMN Extension system.
Thank you to our farm and ag professional partners for contributions to the UMN Fruit Update series. Non-credited photos in this article were either taken by Madeline Wimmer or within the UMN Extension system.
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